Change the default build dir to 'build'

Also add '.mbedignore' to ensure that contents of build are not
scanned/included by the build system and reflect the change in the documentation

Author: screamerbg

README.md

@@ -339,15 +339,15 @@ Allocated Stack: 32768 bytes
 Total Static RAM memory (data + bss): 10788 bytes
 Total RAM memory (data + bss + heap + stack): 109096 bytes
 Total Flash memory (text + data + misc): 66014 bytes
-Image: .build/K64F/GCC_ARM/mbed-os-program.bin
+Image: build/K64F/GCC_ARM/mbed-os-program.bin
 ```
 
 The arguments for *compile* are:
 
 * `-m <MCU>` to select a target.
 * `-t <TOOLCHAIN>` to select a toolchain (of those defined in `mbed_settings.py`, see above). The value can be either `ARM` (ARM Compiler 5), `GCC_ARM` (GNU ARM Embedded), or `IAR` (IAR Embedded Workbench for ARM).
 * `--source <SOURCE>` to select the source directory. The default is `.` (the current directorty). You can specify multiple source locations, even outside the program tree.
-* `--build <BUILD>` to select the build directory. Default: `.build/` inside your program.
+* `--build <BUILD>` to select the build directory. Default: `build/` inside your program.
 * `--options <OPTIONS>` to select compile options. Examples: "debug-info": will generate debugging information; "small-build" will use microlib/nanolib, but limit RTOS to single thread; "save-asm": will save the asm generated by the compiler
 * `--library` to compile the code as a [static .a/.ar library](#compiling-static-libraries).
 * `--config` to inspect the run-time compile configuration (see below).
@@ -357,7 +357,7 @@ The arguments for *compile* are:
 * `-v` or `--verbose` for verbose diagnostic output.
 * `-vv` or `--very_verbose` for very verbose diagnostic output.
 
-The compiled binary, ELF image, memory usage and link statistics can be found in the `.build` subdirectory of your program.
+The compiled binary, ELF image, memory usage and link statistics can be found in the `build` subdirectory of your program.
 
 ### Compiling static libraries
 
@@ -479,7 +479,7 @@ Allocated Stack: 32768 bytes
 Total Static RAM memory (data + bss): 6568 bytes
 Total RAM memory (data + bss + heap + stack): 104876 bytes
 Total Flash memory (text + data + misc): 48357 bytes
-Image: .build\tests\K64F\GCC_ARM\TESTS\mbedmicro-rtos-mbed\mutex\TESTS-unit-myclass.bin
+Image: build\tests\K64F\GCC_ARM\TESTS\mbedmicro-rtos-mbed\mutex\TESTS-unit-myclass.bin
 ...[SNIP]...
 mbedgt: test suite report:
 +--------------+---------------+---------------------------------+--------+--------------------+-------------+
@@ -509,14 +509,14 @@ The arguments to `test` are:
 * `--run` to only run the tests
 * `-n <TESTS_BY_NAME>` to limit the tests built or ran to a comma separated list (ex. test1,test2,test3)
 * `--source <SOURCE>` to select the source directory. Default is `.` (the current dir). You can specify multiple source locations, even outside the program tree.
-* `--build <BUILD>` to select the build directory. Default: `.build/` inside your program.
+* `--build <BUILD>` to select the build directory. Default: `build/` inside your program.
 * `--options <OPTIONS>` to select compile options. Examples: "debug-info": will generate debugging information; "small-build" will use microlib/nanolib, but limit RTOS to single thread; "save-asm": will save the asm generated by the compiler
 * `-c or --clean` to clean the build directory before compiling,
 * `--test-spec <TEST_SPEC>` to set the path for the test spec file used when building and running tests (the default path is the build directory).
 * `-v` or `--verbose` for verbose diagnostic output.
 * `-vv` or `--very_verbose` for very verbose diagnostic output.
 
-The compiled binaries and test artifacts can be found in the `.build/tests/<TARGET>/<TOOLCHAIN>` directory of your program.
+The compiled binaries and test artifacts can be found in the `build/tests/<TARGET>/<TOOLCHAIN>` directory of your program.
 
 #### Finding available tests
 
@@ -539,9 +539,9 @@ You can find the tests that are available for **running** by using the `--run-li
 
 ```
 $ mbed test --run-list
-mbedgt: test specification file '.\.build/tests\K64F\ARM\test_spec.json' (specified with --test-spec option)
-mbedgt: using '.\.build/tests\K64F\ARM\test_spec.json' from current directory!
-mbedgt: available tests for built 'K64F-ARM', location '.\.build/tests\K64F\ARM'
+mbedgt: test specification file '.\build\tests\K64F\ARM\test_spec.json' (specified with --test-spec option)
+mbedgt: using '.\build\tests\K64F\ARM\test_spec.json' from current directory!
+mbedgt: available tests for built 'K64F-ARM', location '.\build\tests\K64F\ARM'
         test 'TESTS-functional-test1'
         test 'TESTS-functional-test2'
         test 'TESTS-functional-test3'
@@ -594,7 +594,7 @@ mbed-os-program
  |     `- host_tests      # Python host tests script directory
  |        |- host_test1.py
  |        `- host_test2.py
- `- .build                # Build directory
+ `- build                 # Build directory
      |- <TARGET>          # Target directory
      | `- <TOOLCHAIN>     # Toolchain directory
      |   |- TestCase1.bin # Test binary

mbed/mbed.py

@@ -53,6 +53,7 @@
     "*.orig",
 
     # mbed Tools
+    "build",
     ".build",
     ".export",
 
@@ -1118,6 +1119,7 @@ class Program(object):
     is_cwd = False
     is_repo = False
     is_classic = False
+    build_dir = "build"
 
     def __init__(self, path=None, print_warning=False):
         path = os.path.abspath(path or os.getcwd())
@@ -1343,6 +1345,18 @@ def get_macros(self):
                 macros = f.read().splitlines()
         return macros
 
+    def ignore_build_dir(self):
+        build_path = os.path.join(self.path, self.build_dir)
+        if not os.path.exists(build_path):
+            os.mkdir(build_path)
+        if not os.path.exists(os.path.join(build_path, '.mbedignore')):
+            try:
+                with open(os.path.join(build_path, '.mbedignore'), 'w') as f:
+                    f.write('*\n')
+            except IOError:
+                error("Unable to write build ignore file in \"%s\"" % os.path.join(build_path, '.mbedignore'), 1)
+
+
 # Global class used for global config
 class Global(object):
     def __init__(self):
@@ -2005,7 +2019,7 @@ def status_(ignore=False):
     dict(name='--config', dest='compile_config', action='store_true', help='Show run-time compile configuration'),
     dict(name='--prefix', dest='config_prefix', action='append', help='Restrict listing to parameters that have this prefix'),
     dict(name='--source', action='append', help='Source directory. Default: . (current dir)'),
-    dict(name='--build', help='Build directory. Default: .build/'),
+    dict(name='--build', help='Build directory. Default: build/'),
     dict(name=['-c', '--clean'], action='store_true', help='Clean the build directory before compiling'),
     dict(name=['-N', '--artifact-name'], help='Name of the built program or library'),
     dict(name=['-S', '--supported'], dest='supported', action='store_true', help='Shows supported matrix of targets and toolchains'),
@@ -2017,6 +2031,7 @@ def compile_(toolchain=None, target=None, options=False, compile_library=False,
     # Find the root of the program
     program = Program(os.getcwd(), True)
     program.check_requirements(True)
+    program.ignore_build_dir()
     # Remember the original path. this is needed for compiling only the libraries and tests for the current folder.
     orig_path = os.getcwd()
 
@@ -2052,7 +2067,7 @@ def compile_(toolchain=None, target=None, options=False, compile_library=False,
     elif compile_library:
         # Compile as a library (current dir is default)
         if not build:
-            build = os.path.join(os.path.relpath(program.path, orig_path), '.build', 'libraries', os.path.basename(orig_path), target, tchain)
+            build = os.path.join(os.path.relpath(program.path, orig_path), program.build_dir, 'libraries', os.path.basename(orig_path), target, tchain)
 
         popen(['python', '-u', os.path.join(tools_dir, 'build.py')]
               + list(chain.from_iterable(izip(repeat('-D'), macros)))
@@ -2068,7 +2083,7 @@ def compile_(toolchain=None, target=None, options=False, compile_library=False,
     else:
         # Compile as application (root is default)
         if not build:
-            build = os.path.join(os.path.relpath(program.path, orig_path), '.build', target, tchain)
+            build = os.path.join(os.path.relpath(program.path, orig_path), program.build_dir, target, tchain)
 
         popen(['python', '-u', os.path.join(tools_dir, 'make.py')]
               + list(chain.from_iterable(izip(repeat('-D'), macros)))
@@ -2095,7 +2110,7 @@ def compile_(toolchain=None, target=None, options=False, compile_library=False,
     dict(name='--run', dest='run_only', action='store_true', help='Only run tests'),
     dict(name=['-n', '--tests-by-name'], dest='tests_by_name', help='Limit the tests to a list (ex. test1,test2,test3)'),
     dict(name='--source', action='append', help='Source directory. Default: . (current dir)'),
-    dict(name='--build', help='Build directory. Default: .build/'),
+    dict(name='--build', help='Build directory. Default: build/'),
     dict(name=['-o', '--options'], action='append', help='Compile options. Examples: "debug-info": generate debugging information; "small-build" to use microlib/nanolib, but limit RTOS to single thread; "save-asm": save the asm generated by the compiler'),
     dict(name=['-c', '--clean'], action='store_true', help='Clean the build directory before compiling'),
     dict(name='--test-spec', dest="test_spec", help="Path used for the test spec file used when building and running tests (the default path is the build directory)"),
@@ -2107,6 +2122,7 @@ def test_(toolchain=None, target=None, compile_list=False, run_list=False, compi
     # Find the root of the program
     program = Program(os.getcwd(), True)
     program.check_requirements(True)
+    program.ignore_build_dir()
     # Save original working directory
     orig_path = os.getcwd()
 
@@ -2126,7 +2142,7 @@ def test_(toolchain=None, target=None, compile_list=False, run_list=False, compi
 
         # Setup the build path if not specified
         if not build:
-            build = os.path.join(program.path, '.build/tests', target, tchain)
+            build = os.path.join(program.path, program.build_dir, 'tests', target, tchain)
 
 
         if test_spec:
@@ -2193,6 +2209,7 @@ def export(ide=None, target=None, source=False, clean=False, supported=False):
     # Find the root of the program
     program = Program(os.getcwd(), True)
     program.check_requirements(True)
+    program.ignore_build_dir()
     # Remember the original path. this is needed for compiling only the libraries and tests for the current folder.
     orig_path = os.getcwd()
     # Change directories to the program root to use mbed OS tools